Methods for inhibiting scale formation

ABSTRACT

A composition for inhibiting scale and methods of using said composition consisting of a relatively water-insoluble organic precipitate formed by the reaction of a water-soluble polyelectrolytic organic polymer having an average molecular weight in the range of from about 1,000 to about 100,000 and a water-soluble organic cationic surface active compound.

This is a division of application Ser. No. 423,638, filed Dec. 10, 1973,now abandoned which is a division of application Ser. No. 218,597, filedJan. 17, 1972, now U.S. Pat. No. 3,832,302, issued Aug. 27, 1974,entitled "Methods for Inhibiting Scale Formation."

This invention relates to preventing the formation of scale in systemscontaining aqueous solutions. The term "scale" is used herein to meandeposits formed on surfaces in contact with aqueous solutions due to theprecipitation of scale forming compounds from the aqueous solutions. Theterm "scale forming compounds" is used herein to mean those compoundscommonly associated with hard water and the brines produced from waterand oil wells, e.g., calcium carbonate, calcium sulfate, barium sulfateand strontium sulfate. Other water-insoluble sulfates and carbonates maybe classified as scale but are usually found in small quantities ascompared with the foregoing compounds.

Water or aqueous solutions containing ionized scale forming compoundsare utilized in many domestic and industrial applications for a varietyof purposes. Because these aqueous solutions are subjected to changes inchemical environment, the scale forming compounds precipitate and aredeposited on the surfaces of the systems within which the aqueoussolutions are contained. The deposition of scale within such systemscauses severe problems among which are the restriction of fluid flow,the reduction of heat transfer, the decrease in equipment life due toexcessive wear, corrosion attack, etc.

The handling of water and brines produced from underground formationspresents particularly severe scale formation problems. For example, thebrines produced from oil wells contain high concentrations of scaleforming compounds, and due to the changes in temperature, pressure andother physical conditions of the brines as they are produced,precipitation and deposition of scale in the producing formation, flowlines, separators and other producing and handling equipment frequentlyoccurs.

In preventing the deposition of scale on equipment surfaces in contactwith aqueous solutions, the utilization of a solid composition whicheffectively inhibits the precipitation of scale forming compounds at lowconcentrations and which is relatively water-insoluble is highlyadvantageous. That is, continuous protection over an extended period oftime can be insured through the use of a slowly soluble solidcomposition introduced into the system containing the aqueous solution.Further, particularly in water and brine producing wells, it isadvantageous to place such an inhibitor in the porous producingformation adjacent to the well bore so that as water and brines areproduced from the formation effective quantities of the inhibitor aredissolved therein thereby insuring prevention of scale deposition inflow lines and on downstream equipment surfaces. The in situ formationof an inhibitor composition in an underground producing formationobviates the heretofore encountered problems associated with squeezinginhibiting agents into well formations whereby large amounts of theinhibiting agents are immediately produced back and wasted.

By the present invention novel liquid additives and solid compositionsare provided which are utilized to prevent the precipitation of scaleforming compounds from aqueous solutions. A liquid additive of thepresent invention is introduced to the system to be protected, and whencontacted by the aqueous solution contained therein, the additive reactsto form, in situ, a solid composition which upon being slowly dissolvedby the aqueous solution substantially prevents the precipitation ofscale therefrom. The solid composition is relatively insoluble inaqueous solutions over a wide pH range, including neutral, stronglybasic and strongly acidic solutions.

When the solid composition is formed in place in a container,particularly a steel vessel or pipeline, it adheres to the confiningwalls of the container to form a coating therein which slowly dissolvesin aqueous solutions over an extended period of time. As the compositiondissolves it reacts with scale forming compounds contained in theaqueous solution to thereby prevent the formation of scale within thecontainer. Containers having structural materials other than steel andvarious other materials to which the reaction product will adhereinclude clays, salts, sand, sandstone, limestone, dolomite, glass,gravel, aluminum, enamels, elastomers, straw, vegetable matter and thelike. The fact that the composition adheres to the walls of theconfining container is important in that long term protection againstscale depositions even after the coating has been subjected to theprolonged pressure of strong acidic and basic solutions is obtained.

The liquid additive of the present invention basically comprises amixture of a water-soluble polyelectrolytic organic polymer having anaverage molecular weight in the range of from about 1,000 to 100,000 anda water-soluble organic cationic surface active compound. When added toan excess of water or aqueous solution, the mixed components of theadditive react to form the relatively water-insoluble solid compositionof the present invention. The solid composition is an organic complexwhich upon dissolution is effective in small quantities for inhibitingthe precipitation of scale forming compounds from aqueous solutions.

Among the polyelectrolytic organic polymers suitable for use inaccordance with the present invention are the polymers of compoundshaving the formula ##STR1## wherein

R is selected from the group consisting of hydrogen or a methyl radical,and

R₁ is selected from the group consisting of nitrile, amide and carboxylradicals; and the water soluble salts thereof.

For example, homopolymers and copolymers of acrylic acid, methacrylicacid, acrylamide and methacrylamide, the alkali metal and ammonium saltsof the polymers and mixtures of the salts and polymers are particularlysuitable. In addition, polymers of the N-alkyl substituted amides, theN-aminoalkylamides, and the corresponding N-alkylaminoalkyl substitutedamides may be utilized. Polymers of the aminoalkyl acrylates, theaminoalkyl methacrylamides, and the N-alkyl substituted aminoalkylesters of either acrylic or methacrylic acids may be utilized as well ascopolymers of the foregoing compounds with other copolymerizing monomerssuch as ethylene, propylene, isobutylene, etc. In general, ethylenicpolyelectrolytic organic polymers having numerous side chainsdistributed along a substantially continuous carbon atom molecule may beutilized in accordance with the present invention. The side chains maybe hydrocarbon groups, carboxylic acid groups or derivatives thereof,sulfonic acid groups or derivatives thereof, phosphoric acid orderivatives thereof, heterocyclic nitrogen groups, aminoalkyl groups,alkoxy radicals and other organic groups. The number and the relativeproportions of the hydrophilic and hydrophobic groups must be such thata water-soluble polymeric compound having a substantially large numberof ionizable radicals results. Generally, the higher the molecularweight of the polymer the less water-soluble it is. However, polymersbeing average molecular weights of from 1,000 up to about 100,000 may beutilized. Polymers having an average molecular weight of from about1,000 to 30,000 are preferred and those having average molecular weightsof from 1,000 to 10,000 are most preferred.

The water-soluble polyelectrolytic organic polymers preferred for use inthe present invention are those selected from the group consisting ofhomopolymers and copolymers of acrylic acid, methacrylic acid,acrylamide and methacrylamide, the alkali metal and ammonium salts ofsaid polymers and mixtures of said polymers and salts. A homopolymer ofacrylic acid wherein about 70% of the active hydrogen atoms have beenreplaced by sodium ions having an average molecular weight in the rangeof from about 1,000 to about 10,000 is most preferred.

A great variety of water-soluble organic cationic surface activecompounds are commercially available and may be used in accordance withthe present invention. For example, aliphatic (fatty) amines and theirderivatives, e.g., the dimethyl dodecylamine oxide acetate of tertiaryfatty amines; homologues of aromatic amines having fatty chains, e.g.,dodecylaniline; fatty amides derived from aliphatic diamines, e.g.,1-hydroxyethyl-2-heptadecenyl glyoxacline; and fatty amides derived fromdisubstituted amines, e.g., the formate of an oleyl amide derivative ofethylene diamine. In addition, a variety of quaternary ammoniumcompounds may be utilized having the general formula ##STR2## wherein

R₂ represents hydrogen or an alkyl radical having from 1 to 20 carbonatoms,

R₃ represents an alkyl or aryl radical having from 1 to 20 carbon atoms,and

A is an anion selected from the group consisting of halide, acetate,sulfate, nitrate and hydroxide,

and mixtures of the compounds. Examples of such quaternary ammoniumcompounds include trimethyl-1-methyl-n-pentadecylammonium chloride,trimethyl-n-octadecylammonium bromide,trimethyl-1-methyl-n-nonadecylammonium acetate,trimethyl-n-octylammonium hydroxide, trimethyl-n-dodecylammoniumnitrate, and trimethyl-n-decylammonium sulfate.

Other organic cationic surface active compounds useful in accordancewith the present invention are those ammonium compounds derived fromfatty amides of disubstituted diamines such as monstearyl ethylenediamine and triethyl ammonium methyl sulfate as well as ammoniumcompounds of the benzimidazolines such as methylheptadecyl benzimidazolhydrobromide and heptadecyl N-benzyl benzimidazol. Basic compounds orpyridinium and its derivatives may be utilized such as cetyl pyridiniumchloride and octadecyl pyridinium hydrobromide. Basic compounds ofsulfonium phosphonium and antimonium, e.g., octadecyl sulfonium methylsulfate, and the urethanes or basic salts of ethylene diamine such as asteric acid condensate with diethylene triamine may also be used.

Preferred organic cationic surface active compounds for use inaccordance with the present invention are as follows:

a. an amine having the following formula ##STR3## wherein R₄ representshydrogen or an alkyl radical having from 8 to 18 carbon atoms and R₅represents an alkyl radical having from 8 to 18 carbon atoms,

b. a primary alkyl amine acetate having the following formula ##STR4##wherein R₆ represents an alkyl radical having from 8 to 18 carbon atoms,

c. an alkyl trimethylene diamine having the following formula

    NH.sub.3 (CH.sub.2).sub.3 NHR.sub.7

wherein R₇ represents an alkyl radical having from 8 to 18 carbon atoms,and

d. a quaternary ammonium compound having the following formula ##STR5##wherein R₈ represents hydrogen or an alkyl radical having from 1 to 20carbon atoms, R₉ represents an alkyl or aryl radical having from 1 to 20carbon atoms, and X represents a halide.

Mixtures of the above compounds may also be used.

The most preferred water-soluble organic cationic surface activecompounds for use in accordance with the present invention arequaternary amonium chloride compounds or mixtures thereof having thefollowing formula ##STR6## wherein

R' represents hydrogen or an alkyl radical having from 1 to 20 carbonatoms and

R" represents an alkyl or aryl radical having from 1 to 20 carbon atoms.

Examples of these compounds are myristyl dimethyl benzyl ammoniumchloride, decyl trimethyl ammonium chloride and cetyl trimethyl ammoniumchloride.

In the preparation of the liquid additives of the present invention, thewater-soluble organic cationic surface active compound is mixed with thepolyelectrolytic organic polymer is an amount preferably substantiallyequal to the neutralization equivalent of the organic polymer. The term"neutralization equivalent" is used herein to mean the quantity ofcationic surface active compound required to supply the number ofcations necessary to react with or neutralize the anionic sites on theorganic polymer molecule. While any ratio of cationic surface activecompound to anionic organic polymer may be utilized, the most economicalprocedure is to use a ratio such that the neutralization equivalent ofcationic surface active compound is present, i.e., the resultant mixtureis neutral when dissolved in water. This quantity, of course, varieswith the particular organic polymer utilized, but may be readilydetermined by a variety of conventional methods such as by titrating theorganic polymer to a neutralization end point and then calculatingstoichiometrically the neutralization equivalent based on the particularcationic surface active compound to be used.

The surface active compound useful herein is dispersed in the organicpolymer without a reaction product being formed. However, when theliquid additive mixture is dissolved in water or other aqueous solution,the components thereof, i.e., the organic polymer and surface activecompound, react to form the novel solid composition of the presentinvention, i.e., a relatively water-insoluble organic composition. Thereaction is represented as follows when an acrylic acid polymer and aquaternary ammonium chloride surface active compound are utilized:##STR7##

If desirable, in order to prevent the liquid additive from separatinginto component layers when stored or transported, a small quantity ofwater may be intermixed with the components of the additive in an amountjust sufficient to form the additive into the "precursor" of thereaction product obtained when the mixture is added to an excess ofwater. The term "precursor" of the water-insoluble organic compositionformed by the liquid additive in an excess of water is used to mean thehomogeneous relatively clear liquid which results when a small amount ofwater is added to the mixture of polyelectrolytic organic polymer andorganic cationic surface active compounds described above. While thespecific amount of water required to form the precursor depends upon theparticular polymer and surface active compound utilized in the additivemixture, the amount may readily be determined experimentally. Once theadditive mixture is formed into the homogeneous precursor of the solidinhibitor composition it may be stored for indefinite periods of timewithout deleterious effects.

The solid organic composition of the present invention is very slowlysoluble in aqueous solutions over a broad pH range, i.e., over a pHrange of from 0 to 14, and is particularly suitable as a slow releasescale inhibitor.

The solid composition may be formed by reacting the organic polymer andcationic surface active agent in an excess of water. The precipitate maythen be separated and dried so that a solid inhibitor is obtained whichcan in turn be added directly to the aqueous system to be protected. Ifdesired, however, the composition may be precipitated in the system tobe protected so that it adheres to the system and is slowly dissolvedover a long period of time.

As illustrated by the examples which follow, the solid composition ofthe present invention effectively inhibits or prevents the precipitationof ionized scale forming compounds from aqueous solutions when dissolvedtherein. This is due to the dissolved composition exhibiting what hasheretofore been defined as the "threshold inhibition effect." When a fewparts per million of a threshhold inhibitor are added to an aqueoussolution containing scale forming anionic and cationic components, nointeraction or precipitation occurs between the inhibitor and ioniccomponents of the water, yet the inhibitor prevents the precipitation ofthe ionic components. The threshhold or inhibition property of theorganic inhibitor composition of the present invention is effective whenthe composition is dissolved in an aqueous solution containing ionizedscale forming compounds at concentrations of from about 0.1 parts permillion to about 100 parts per million. The threshhold inhibitionproperty of the dissolved composition stabilizes thousands of parts permillion of scale forming ions due to surface activity and film formationon discreet particles.

The in situ formation of the solid composition of the present inventionmay be carried out using any of a variety of techniques depending uponthe particular system to be protected. For example, if the solidcomposition is to be added to a system containing an aqueous solutionsuch as an evaporative water cooler, a quantity of the liquid additiveof the present invention may be introduced directly into the aqueoussolution in the system and allowed to be contacted and dissolvedthereby. As soon as the liquid additive is dissolved, it reacts to formthe relatively water-insoluble solid composition of the presentinvention which is precipitated in the system and which adheres to theparts of the system in contact with the aqueous solution. The liquidadditive is introduced to the system in a quantity such that an amountof solid precipitate is formed effective to prevent the formation ofscale in the system over a desired period of time. That is, theprecipitate remains in the system and is slowly released or dissolved bythe aqueous solution contained therein thereby inhibiting theprecipitation of scale forming compounds and their deposition onsurfaces in contact with the aqueous solution.

The in situ formation of the solid composition of the present inventionis particularly suitable for preventing the formation of scale in waterand/or brine producing oil and water wells. The liquid additive of thepresent invention can be added in the precursor form to the oil or waterwell in a quantity sufficient to provide the solid precipitate in aneffective amount at or near the bottom of the well. As stated previouslyherein, the effective concentration of the dissolved solid compositionin an aqueous solution is from about 0.1 to 100 parts per million,preferably about 0.25 to 20 parts per million. Thus, the particularquantity of solid composition required to be placed in a well to provideprotection over a desired period of time may be calculated and dependson the particular flow rate of water or aqueous solution produced.

Once placed in the well formation, the inhibitor additive is contactedby water or brine contained therein and dissolved thereby causing therelatively insoluble adhesive organic composition of the presentinvention to be precipitated. When formed, the precipitated compositiondissolves in an amount effective to inhibit the precipitation of scalein the produced water or brine until exhausted. The adhesive propertiesof the composition cause it to adhere to surfaces within the wellformation and resist the washing action of formation fluids as they areproduced.

If desirable, in order to prevent the formation of the solid compositionduring transport of the liquid additive down the well bore, the liquidadditive may be dispersed in a water free carrying fluid such as dieseloil and the dispersion pumped into the formation. After the dispersionis placed in the formation the well is returned to normal production sothat the inhibitor additive is dissolved and the organic compositionformed, or alternatively, a water overflush may be utilized to bringabout the in situ formation of the composition.

Due to the adhesive properties and very low solubility of the solidcomposition it remains in the formation over a long time period and isslowly dissolved in produced water or brine thereby preventing theformation of scale in the formation and production equipment. Further,should remedial acidizing of the formation be required subsequent toplacing the composition of the present invention therein, thecomposition will not be destroyed by the acid treatment.

The following examples are set forth to more clearly illustrate thepresent invention, but are not to be considered as limiting the scope ofthe invention.

EXAMPLE 1

This example illustrates the scale inhibiting effectiveness of the solidorganic composition formed by the reaction of a homopolymer of acrylicacid having about 70% of the active hydrogen ions replaced by sodiumions and having an average molecular weight in the range of from about1,000 to 10,000, and a mixture of alkyl dimethyl quaternary ammoniumchloride compounds wherein the alkyl substituents range from 1 to 20carbon atoms. Mixtures of the polyacrylate and quaternary ammoniumchloride compounds are prepared on a weight basis of 8:1 and 4:1,respectively. Various quantities of the liquid mixtures are then addedto aqueous test solutions containing excess calcium and sulfate ions.After stirring, the test solutions including a blank solution, i.e., atest solution which does not contain inhibitor, are allowed to stand for24 hours at 72° F. At the end of the 24 hour period, aliquots of thetest solutions are taken and the amount of calcium held in the solutionsdetermined by conventional titration procedures. The results of thesetests are shown in Table I.

                  TABLE I                                                         ______________________________________                                        COMPARISON OF 24 HOUR CALCIUM SULFATE SCALE                                   INHIBITION at 72° F FOR VARIOUS INHIBITOR                              CONCENTRATIONS                                                                ______________________________________                                        Inhibitor    Weight Ratio of                                                                             Amount of Calcium                                  Composition  Polymer to Surface                                                                          Ions Held In                                       Concentration (ppm)                                                                        Active Compound                                                                             Solution (ppm)                                     ______________________________________                                        0     (blank test              1600                                                 solution)                                                               5                8:1           1720                                           5                4:1           1760                                           10               8:1           1960                                           10               4:1           1880                                           20               8:1           2240                                           20               4:1           2780                                           50               8:1           4060                                           50               4:1           4060                                           100              8:1           5000                                           100              4:1           5000                                           ______________________________________                                    

From the above table it may be seen that the dissolved solid inhibitorcomposition effectively inhibits the precipitation of calcium sulfate,i.e., holds the calcium ions in solution, and as the concentration ofthe dissolved composition is increased up to 100 ppm the amount ofcalcium ions held in solution increases.

EXAMPLE 2

Polyacrylic acid having about 70% of the active hydrogen atoms replacedby sodium ions and having an average molecular weight in the range offrom about 1,000 to about 10,000 is added to an excess of distilledwater and titrated with 0.2 N-sodium hydroxide to a phenolphthalein endpoint. The neutralization equivalent of N-dodecylamine acetate iscalculated and a mixture of the partially neutralized sodium salt ofpolyacrylic acid and N-dodecylamine acetate is prepared with theN-dodecylamine acetate present in an amount equal to 10% of theneutralization equivalent. The resulting liquid additive mixture isintroduced into test solutions containing excess calcium and sulfateions at various concentrations. A comparison of the amounts of calciumions held in solution after 24 hours at 72° F is given in Table IIbelow.

                  TABLE II                                                        ______________________________________                                        COMPARISON OF 24 HOUR CALCIUM SULFATE SCALE                                   INHIBITION AT 72° F FOR VARIOUS POLYACRYLATE-                          PRIMARY AMINE ACETATE ADDITIVE                                                CONCENTRATIONS                                                                ______________________________________                                        Inhibitor Weight Ratio of    Amount of                                        Additive  Polymer to Surface Active                                                                        Calcium Ions                                     Concentration                                                                           Compound at 10% of Held In                                          (ppm)     Neutralization Equivalent                                                                        Solution (ppm)                                   ______________________________________                                        0         --                 1600                                             1.05      1:0.05             1740                                             5.25      5:0.25             3400                                             10.5      10:0.5             4520                                             21.0      20:1.0             5000                                             ______________________________________                                    

EXAMPLE 3

The test procedure of Example 2 is repeated except thatpolyacrylate-N-dodecylamine acetate inhibitor additives are preparedwith N-dodecylamine acetate concentrations of 25%, 50%, 75% and 100% ofthe calculated neutralization equivalent, respectively. Each of theadditive mixtures are introduced to test solutions containing excesscalcium and sulfate ions. The amount of calcium ions held in solutionafter 24 hours at 72° F is shown in Table III below.

                  TABLE III                                                       ______________________________________                                        COMPARISON OF 24 HOUR CALCIUM SULFATE SCALE                                   INHIBITION AT 72° F FOR POLYACRYLATE-                                  PRIMARY AMINE ACETATE ADDITIVE                                                ______________________________________                                        Inhibitor % Neutralization   Amount of                                        Additive  Equivalent         Calcium Ions                                     Concentration                                                                           N-Dodecylamine     Held In                                          (ppm)     Acetate            Solution (ppm)                                   ______________________________________                                        0         --                 1000                                             11.25     25                 4860                                             12.5      50                 4800                                             13.75     75                 4700                                             15.0      100                5000                                             ______________________________________                                    

EXAMPLE 4

The test procedure of Example 2 is repeated using various organiccompositions formed from a partially neutralized sodium salt ofpolyacrylic acid (70% of active hydrogen ions replaced by sodium ions)having a molecular weight in the range of from 1,000 to 10,000 andvarious cationic surface active agents at various concentrations. Theresults of these tests are shown in Table IV below.

                  TABLE IV                                                        ______________________________________                                        COMPARISON OF 24 HOUR CALCIUM SULFATE                                         SCALE INHIBITION AT 72° F FOR                                          VARIOUS INHIBITOR COMPOSITIONS                                                ______________________________________                                                     %                                                                             Neutralization                                                                            Inhibitor                                                                              Amount of                                                Equivalent  Concen-  Calcium Ions                                Inhibitor    Surface Active                                                                            tration  Held In Solu-                               Composition  Compound    (ppm)    tion (ppm)                                  ______________________________________                                          --         --          0        1600                                        Polyacrylate-                                                                 Coco Trimethy-                                                                             10%         10.7     4320                                        lene Diamine                                                                  Polyacrylate-                                                                 Coco Trimethy-                                                                             100%        17.46    3400                                        lene Diamine                                                                  Polyacrylate-                                                                 Bis-2 Hydroxy-                                                                             10%         10.63    4140                                        ethyl Amine                                                                   Polyacrylate-                                                                 Bis-2 Hydroxy-                                                                             100%        16.4     3000                                        ethyl Amine                                                                   Polyacrylate-                                                                 Dodecyl      10%         12.1     3960                                        Trimethyl                                                                     Ammonium Chloride                                                             Polyacrylate-                                                                 Dodecyl      100%        34.0     3500                                        Trimethyl                                                                     Ammonium Chloride                                                             Polyacrylate-                                                                 Octadecyl    10%         12.6     3690                                        Trimethyl                                                                     Ammonium Chloride                                                             Polyacrylate-                                                                 Octadecyl    100%        36.6     3600                                        Trimethyl                                                                     Ammonium Chloride                                                             Polyacrylate-                                                                 Tallowdicoco 10%         11.58    3600                                        Dimethyl                                                                      Ammonium Chloride                                                             Polyacrylate-                                                                 Tallowdicoco 100%        25.9     3220                                        Dimethyl                                                                      Ammonium Chloride                                                             ______________________________________                                    

From the foregoing it may be seen that the solid organic inhibitorcompositions of the present invention upon dissolution effectivelyinhibit the precipitation of calcium sulfate from aqueous solutions atvarious concentrations and at various ratios of polymer to surfaceactive compound.

EXAMPLE 5

The test procedure of Example 2 is repeated except that the temperatureof the test solutions is maintained at 180° F. The results of thesetests are shown below.

                  TABLE V                                                         ______________________________________                                        COMPARISON OF 24 HOUR CALCIUM SULFATE                                         SCALE INHIBITION AT 180° F FOR                                         VARIOUS INHIBITOR COMPOSITIONS                                                ______________________________________                                                      Inhibitor    Amount of                                                        Composition  Calcium Ions                                       Inhibitor     Concentration                                                                              Held In                                            Composition   (ppm)        Solution (ppm)                                     ______________________________________                                          --          0            1450                                               Polyacrylate-                                                                 N-Dodecyl     5.25         1530                                               Amine Acetate                                                                 Polyacrylate-                                                                 N-Dodecyl     10.5         1760                                               Amine Acetate                                                                 Polyacrylate-                                                                 Dodecyl Trimethyl                                                                           6.09         1630                                               Ammonium Chloride                                                             Polyacrylate-                                                                 Dodecyl Trimethyl                                                                           12.1         1700                                               Ammonium Chloride                                                             ______________________________________                                    

EXAMPLE 6

The test procedure of Example 2 is repeated except that the testsolutions contain an excess of calcium and carbonate ions. The resultsof these tests are shown in Table VI.

                  TABLE VI                                                        ______________________________________                                        COMPARISON OF 24 HOUR CALCIUM CARBONATE                                       SCALE INHIBITION AT 72° F FOR                                          VARIOUS INHIBITOR COMPOSITIONS                                                ______________________________________                                                      Inhibitor    Amount of                                                        Composition  Calcium Ions                                       Inhibitor     Concentration                                                                              Held In                                            Composition   (ppm)        Solution (ppm)                                     ______________________________________                                          --          0            25                                                 Polyacrylate-                                                                 N-Dodecyl     5.25         70                                                 Amine Acetate                                                                 Polyacrylate-                                                                 N-Dodecyl     10.5         80                                                 Amine Acetate                                                                 Polyacrylate-                                                                 Alkyl Dimethyl                                                                              7.1          70                                                 Benzyl Ammonium                                                               Chloride                                                                      Polyacrylate-                                                                 Alkyl Dimethyl                                                                              14.2         70                                                 Benzyl Ammonium                                                               Chloride                                                                      ______________________________________                                    

EXAMPLE 7

The static water solubility of a polyacrylate inhibitor composition ofthe present invention is compared to the static water solubility of acalcium salt of the same polyacrylic acid. The results of the comparisonare shown in Table VII below.

                  TABLE VII                                                       ______________________________________                                        TEST CONDITIONS:                                                              STATIC TAP WATER MAINTAINED AT 72° F                                   ______________________________________                                                                 Concentration of                                                              Inhibitor Dissolved                                  Inhibitor                In Water At End Of                                   Composition  Test Period Test Period (ppm)                                    ______________________________________                                        Polyacrylate-                                                                 Myristyl Dimethyl                                                                          21 days     200                                                  Benzyl Ammonium                                                               Chloride                                                                      Calcium Salt of                                                               Polyacrylic Acid                                                                           24 hours    968                                                  ______________________________________                                    

From Table VII it may be seen that the solid inhibitor composition ofthe present invention is insoluble to a greater degree than thepolyacrylic acid salts, and as a result, is more efficient andeconomical when utilized as a slow release scale inhibitor.

EXAMPLE 8

The solid inhibitor composition formed by the reaction of polyacrylicacid having 70% of the active hydrogen ions replaced with sodium ionsand an average molecular weight between 1,000 and 10,000 and a mixtureof alkyl dimethyl quaternary amonium chloride compounds wherein thealkyl substituents range from 1 to 20 carbon atoms is prepared. Inaddition, the calcium salt of the same partially neutralized polyacrylicacid is prepared. Various acid and alkaline solutions are prepared and 2gm amounts of the calcium polyacrylate salt and the solidpolyacrylate-surface active compound composition are added to separate200 cc portions of the solutions. The test solutions are observed for 24hours to determine the solubility of the compositions therein. Theresults of these tests are shown in Table VIII below.

                                      TABLE VIII                                  __________________________________________________________________________    SOLUBILITY OF VARIOUS COMPOSITIONS                                            IN VARIOUS ACID AND ALKALINE SOLUTIONS                                         Solvent       Solvent pH                                                                           Composition Tested                                                                             Remarks                                __________________________________________________________________________    15% Hydrochoric Acid                                                                         less than 1                                                                          Polyacrylate-Surface Active                                                                   Only Slightly Dissolved                                       Compound Composition                                    15% Hydrochloric Acid                                                                        less than 1                                                                          Calcium Polyacrylate Salt                                                                     Completely Dissolved                    5% Hydrochloric Acid                                                                         less than 1                                                                          Polyacrylate-Surface Active                                                                   Only Slightly Dissolved                                       Compound Composition                                    5% Hydrochloric Acid                                                                         less than 1                                                                          Calcium Polyacrylate Salt                                                                     Completely Dissolved                    5% Acetic Acid less than 1                                                                          Polyacrylate-Surface Active                                                                   Only Slightly Dissolved                                       Compound Composition                                    5% Acetic Acid less than 1                                                                          Calcium Polyacrylate Salt                                                                     Completely Dissolved                    1.0 N Sodium Hydroxide                                                                       14     Polyacrylate-Surface Active                                                                   Only Slightly Dissolved                                       Compound Composition                                    1.0 N Sodium Hydroxide                                                                       14     Calcium Polyacrylate Salt                                                                     Completely Dissolved                    0.1 N Sodium Hydroxide                                                                       14     Polyacrylate-Surface Active                                                                   Only Slightly Dissolved                                       Compound Composition                                    0.1 N Sodium Hydroxide                                                                       14     Calcium Polyacrylate Salt                                                                     Completely Dissolved                    1.0 N Potassium Hydroxide                                                                    14     Polyacrylate-Surface Active                                                                   Only Slightly Dissolved                                       Compound Composition                                    1.0 N Potassium Hydroxide                                                                    14     Calcium Polyacrylate Salt                                                                     Completely Dissolved                    0.1 N Potassium Hydroxide                                                                    14     Polyacrylate-Surface Active                                                                   Only Slightly Dissolved                                       Compound Composition                                    0.1 N Potassium Hydroxide                                                                    14     Calcium Polyacrylate Salt                                                                     Completely Dissolved                    __________________________________________________________________________

EXAMPLE 9

An oil well completed open hole at a depth of 10,200 feet in the Pennformation produces 80 barrels of oil and 60 barrels of brine per day.The well production is completely shut off every 90 days due to theformation of calcium carbonate scale and treatment with acid is requiredin order to free the pump for pulling followed by a clean-up job.

After acidizing and clean-up, 80 gallons of a liquid additive comprisedof a mixture of a partially neutralized sodium salt of polyacrylic acidhaving an average molecular weight in the range of from 1,000 to 10,000and an alkyl dimethyl quaternary ammonium chloride surface activecompound is introduced to the producing formation followed by 2,000gallons of fresh water. After the well is shut-in overnight, productionis resumed and the well produces a steady 80 barrels of oil and 60barrels of brine per day on a continuous basis for 9 months withoutacidizing treatments being necessary.

What is claimed is:
 1. A liquid additive for inhibiting theprecipitation of scale forming compounds from aqueous solutionsconsisting essentially of a mixture of a homopolymer of acrylic acidwherein about 70% of the active hydrogen ions are replaced by sodiumions, said polymer having an average molecular weight in the range offrom about 1,000 to about 10,000, and a water-soluble organic cationicsurface active compound selected from the group consisting of:a primaryalkylamine acetate having the following formula ##STR8## wherein R₆represents an alkyl radical having from 8 to 18 carbon atoms, aquaternary ammonium compound having the following formula ##STR9##wherein R₈ represents hydrogen or an alkyl radical having from 1 to 20carbon atoms, R₉ represents a benzyl radical and X represents a halide,and mixtures of said compounds wherein said water-soluble organiccationic surface active compound is present in said additive in anamount substantially equal to the neutralization equivalent of saidacrylic acid polymer.
 2. The additive of claim 1 wherein saidwater-soluble organic cationic surface active compound is saidquaternary ammonium compound.
 3. The additive of claim 2, wherein saidwater-soluble organic cationic surface active compound is myristyldimethyl benzyl ammonium chloride.
 4. The additive of claim 2 whereinwater is present in said additive in an amount sufficient to form theprecursor of the relatively water-insoluble solid reaction productformed when said additive is dissolved in an excess of water but not inan amount sufficient to bring about the precipitation of said relativelywater-insoluble reaction product.
 5. The additive of claim 3 whereinwater is present in said additive in an amount sufficient to form theprecursor of the relatively water-insoluble solid reaction productformed when said additive is dissolved in an excess of water but not inan amount sufficient to bring about the precipitation of said relativelywater-insoluble reaction product.